In recent years, attention has been paid to plant-derived resins as a substitute for petroleum-derived resins, and active investigations have been made on the practical use of resin compositions using such plant-derived resins. In recent years, attention has been paid particularly to biodegradable resins (including a polylactic acid), as a resin composition using a plant-derived resin, and these biodegradable resins are being commercialized in various applications. The applications of the biodegradable resins are highly diversified from those applications in which the use period of the resins is short and they are disposed after use, such as packaging for container, film for agricultural use, and the like, to those applications requiring high function in which the initial properties of the resins can be maintained for a long period, such as housing for home electric appliance or OA apparatus, automotive part, and the like.
However, the plant-derived resins generally burn easily and cause a disaster and threatens the people' safety; therefore, when they are used in applications requiring a high degree of flame retardancy, such as housing for home electric appliance or OA apparatus, automotive part, and the like, flame retardancy is required to be improved. When a resin composition containing a plant-derived resin is used particularly in a casing for electric appliance, the resin composition must satisfy flame retardancy standards including the UL Standard of U.S.A. However, conventional resin compositions containing a plant-derived resin have been unable to satisfy the above flame retardancy standards.
For making flame-retardant a resin, there is generally considered a method of adding, to a resin, a halogen-based flame retardant (e.g. a bromine compound) high in flame retardancy efficiency. When this halogen-based flame retardant is added to a polycarbonate resin, which typifies polyester resins, however, there is a problem that the resin is deteriorated when subjected to repeated melting and kneading for the purpose of reuse, resulting in a reduction in properties such as flame retardancy, impact resistance and the like. Therefore, when the halogen-based flame retardant is added to a polylactic acid resin containing ester bond (which typifies plant-derived resins), there has been a fear that, when subjected to repeated melting and kneading, the polylactic acid resin gives rise to a reduction in properties similarly to the above-mentioned case of polycarbonate resin.
Meanwhile, there is disclosed, in Patent Literature 1, a biodegradable resin composition obtained by adding, to a polylactic acid resin, at least one kind of flame retardant additive selected from phosphorus compounds, hydroxide compounds (they are referred to also as metal hydrates and include aluminum hydroxide) and silica compounds.
In the Patent Literature 1, phosphorus compounds are shown as an example of the flame retardant additive. While the phosphorus compounds generally plasticize a resin easily and are very effective for the resin's improvement in fluidity, there have been cases that this easy plasticization reduces the heat resistance [in particular, heat distortion temperature (HDT)] and mechanical properties of phosphorus compound-containing resin composition.
Patent Literature 1: JP-A-2003-192925